Plastic Smoothie - DIY Plastic Recycling

Plastic Smoothie is a collaborative project with a very simple goal: giving plastic waste a new life.

Plastic Smoothie started as a personal experiment related to digital fabrication and 3D printing, and it has been partly developed in TecnoLab La Rueca Asociación during my free time with the help of some Patreon supporters and some very creative contributors.

The starting point was the need to find an easy and affordable way to recycle plastic in a maker environment. The Precious Plastic project is a great role model, but their machines and recycling process can be quite complex and expensive if one doesn’t have the equipment.

Project philosophy:

Affordable: we are trying to use electrical appliances for most of the project due to the reduced cost and availability.
Accessible: the machines should be easily found in stores or online and their use shouldn’t be difficult.
Open: this project is shared under a Creative Commons license and anyone can be part of it.

We’ve divided the project into different stages to be sure we stay the course and have clear goals:

Stage 1: simple melting process and 2D models
Stage 2: silicone molds and plastic testing
Stage 3: wow, we got really far!

This instructable corresponds to our experience during the last 3 months working on stage 1.

Step 1: Materials

As we mentioned, we have tried to use electrical appliances in most of the process due to the reduced price and how easy it is to find them.

Unfortunately, in stage 1 we have also used a laser cutter to make the different items, and the price and accessibility of that machine may make it difficult to replicate this project if you don’t have a FabLab or Maker space in your city.

Here’s the list of materials used during stage 1. Small tools such as cutters, plastic bags, and cardboard boxes aren’t included.

Plastic waste. We used PLA plastic during stage 1. It was obtained from failed or old objects made with a 3D printer. It is very easy to work with PLA. Cost: 0€.
Blender (1250W). Cost: 44€ (http://amzn.to/2Fd8DAH)
Mini Oven. Cost: 15€ (second hand) (http://amzn.to/2titpNK)
Oven paper. Cost: 2€
Wood panels (40x30x0.3cm). Cost: 1€ (two units)
Laser cutter. Epilog Mini 18 40W. Cost: +2000€

Price. We have tried to keep our budget under 150€ including electrical appliances, consumables, and plastic. However, the laser cutting machine adds at least 2000€ to the budget. For this reason, we will make a special effort to meet our budget limit in stage 2, focusing on experimenting and learning on stage 1.

Many people recommended us using a meat grinder instead of a blender to shred plastic due to the kind of motor it uses. We decided to go with the blender as it allows us to shred bigger plastic parts, but depending on where you source the plastic waste, it may be a better choice to get a meat grinder or a machine with a high torque motor with some blades.

Here are some tips we would have liked to know before starting this:

If you buy a second-hand oven, it’s highly recommended if it comes with an oven plate. Our mini oven didn’t have one, and it’s more difficult to get perfectly flat plastic panels.
Even though we purchased a new blender for the project, we recommend using an old blender. You won’t be able to use it with food after shredding plastic, it’s almost impossible to clean.
Our blender’s blades got damaged after shredding a little bit less than 10kg of plastic. We don’t recommend shredding big plastic parts. We usually cut them into smaller pieces to make sure the blender doesn’t get damaged.
We’ve tried both silicone mats and oven paper. We bend the edges of the oven paper so there aren’t any spills, but they can only be used twice based on our experience. Silicone mats last longer, but for the moment we haven’t tried to find any way to bend them, and they’re limited.

Step 2: Shredding Plastic

There are many ways of shredding plastic, and in some cases, it isn’t even necessary.

We used a blender with a 1250W motor, and we were careful not to shred parts that were too big or dense (high infill percentage in case the object was 3D printed).

We only used PLA plastic obtained from 3D printed objects or old filament. We separated the filaments depending on the color (grayscale, blue, warm colors…), but the material properties are the same. In this project, we pay special attention to the aesthetic value of the items made, and the shredding process has a key role when deciding which colors and textures you want to create.

As you can see in the next steps, we did some plastic panels with three different visual textures.

Using PLA filament. We cut it in short pieces by hand as it tangled with the blender’s blades. It has a nice retro look.
Large plastic bits. We used medium and large size plastic bits and you can still recognize some parts of the objects that were shredded.
Small plastic bits. We only used the smallest plastic bits (around 5mm).

Step 3: Melting Process

We used a second-hand mini oven to melt the plastic. It only had an oven grid, but it would have been a lot easier if it had had an oven plate.

We used oven paper for most of our tests. We cut an oven paper sheet and we bent the sides to avoid any spills. We tried silicone mats, but we didn’t bend the sides and they were difficult to use.

We made different tests, and the most consistent results we got were the following:

Use medium and small size plastic bits.
Create a consistent thickness on the oven plate with oven paper. We tried to get a 3mm thickness.
Preheat the oven to 190-200 C.
Leave in the oven for 20-25 minutes.

After making more than 30 plastic panels we refined the process and we tried to simplify it. In order to achieve that, we recommend the following:

Melting smaller plastic bits is a lot easier. They melt faster, the panel thickness is more consistent, and there are no bubbles.
Large plastic bits and full 3D printed parts take longer to melt and there are higher chances of getting bubbles inside the plastic, which ruin the panel in some cases.
If you have plastic bits of different sizes, place the bigger ones in the center of the open plate and the smaller ones on the edges. This will help during the melting process.
Control the process and find the sweet spot after the moment where the plastic bits on the edges melt and before you see any bubbles.

Step 4: Pressing Procedure

There are many ways to press the plastic panels, and we did it as DIY as possible. However, there’s one thing to have into account: you need to do this fast.

Our pressing procedure is the following one, and depending on your equipment and space available you may find better ways of doing this.

Once you remove the plastic panel from the oven, it will solidify very fast. It’s important to use gloves and any safety elements you may need, as the plastic is still very hot. When PLA is hot it’s not liquid, just a little bit soft.
Remove the plastic panel with the oven paper below. Both parts are stuck while the plastic panel is not cooled down.
Put both parts (plastic panel and oven paper) on top of a flat wood panel, and then we cover it again with oven paper (or silicone mat).
Put another wood panel on top of it and we add as much weight as we can.
Wait around 10 minutes until the panel cools down.
Remove the oven paper and we have a plastic panel!

Even though the pressing procedure looks easy, it was the most challenging part. There are some things we learned the hard way, and we don’t want any of you to repeat our mistakes:

The plastic panel edges warp as in 3D printing when they cool down. The solution we found is to cool down the panel during the pressing procedure.
We don’t recommend re-using oven paper more than 2 or 3 times. After that, it will be hard to remove and it may ruin a plastic panel.
If you want to get a consistent thickness, we recommend to add some wood/plastic plaques with the desires thickness on the sides of the hot plastic panel. We wanted to get 3mm thickness panels, and what we did was to put some small 3 mm thickness wood plaques on the sides of the hot panel before adding the weight during the pressing procedure. We got very good results with it, even though the edges may be a little bit under 3mm.
If the pressing procedure goes wrong, you just need to melt the plastic panel again and repeat the process!

Step 5: Laser Cutting

We used an Epilog Laser Mini 18 40W to cut the 3mm plastic panels we previously made.

We used the same settings we would use for 3mm acrylic, but we had to increase the laser power when engraving as the engraved part isn't very visible because of the visual pattern.

Also, the laser melts the edges a little bit, but we found it a little bit difficult to get rid of that when laser cutting. You can easily post-process PLA plastic sanding the edges or painting them.

Step 6: Plastic Smoothie Designs

Of course, this project would be meaningless if there weren’t any designs we could make with this technique. For this reason, we’ve made a very small (but full of love) object collection that can be made.

Spirograph. We recommend using thin plastic panels (2mm works great)
Rocket. This model requires a very consistent panel thickness of around 2.5-3mm.
Animal Rings. The inner diameter is 17.5mm(7.5 US size)
Coasters. Yes, they’re just (super useful) circles!

Step 7: What's Next?

I’d like to thank all my Patreon supporters, TecnoLab La Rueca Asociación, and all the people that have contributed in many different ways for making this project possible.

If you’re reading this it means stage 1 is finished, and now we will move to stage 2, where we will change the laser cutting machine and plastic panels for high-temperature molds!